Storage Materials: Determining Purity of Polyester Films for Use in Encapsulation of Collection Materials
Background:
One of the most frequently used housing materials for the protective encapsulation of traditional (paper) materials is film made of the polyester poly (ethylene terephthalate) (PET). The LC Preservation Directorate provides a public service specification for PET film: Specifications for Polyester: Poly(ethylene-terephthalate) Film for the Storage of Artifacts, (500-500 - 2016) [PDF: 115 KB / 2 p.]. This specification states that the film must not contain any plasticizers, surface coatings, UV inhibitors, adsorbents, or coloring agents, and it must be guaranteed to be non-yellowing with age. Thus, it is important that all PET film be of high purity without deleterious contaminants to ensure no damage to Library collection items that come into contact with this material.
Contributing Studies:
Polyester Film Encapsulation. Preservation Office, Library of Congress, 1980.
Hengemihle, Frank H., Lindsey, Norris, and Chandru J. Shahani. Accelerated Aging of Paper Within Plastic Film Envelopes and Cardboard Boxes. In Abstracts of Papers Presented at the Seventeenth Annual Meeting, Cincinnati, Ohio, May 31-June 4, 1989, 59-60. Washington, D.C.: American Institute for Historic and Artistic Works, 1989.
Shahani, C.J. "Aging of Paper Sealed within Polyester Film", Accelerated Aging of Paper: Can it Really Foretell the Permanence of Paper . Preservation Research and Testing Series No.9503, Preservation Research and Testing Office, November 1995.
Arnaud, C.H., Taking Mass Spec Into The Open: Open-air Ionization Methods Minimize Sample Prep and Widen Range of Mass Spectrometry Applications, Chemical & Engineering News, October 8, 2007 Cover, Vol. 85, Issue 41, pp. 13-18.
Shahani, C.J. "Aging of Paper Sealed within Polyester Film", Accelerated Aging of Paper: Can it Really Foretell the Permanence of Paper . Preservation Research and Testing Series No.9503, Preservation Research and Testing Office, November 1995.
Project Description: A manufacturer of PET film opened new factories in China and requested that the Library analyze the film to ensure that it meets Library of Congress specifications. Fourier-transform infrared spectroscopy (FTIR) is routinely used for the analysis of PET and other housing materials. In this research, both FTIR and direct analysis in real time mass spectrometry (DART-MS) were used to analyze the PET film.
Outcomes/Findings: The FTIR spectra gave no indication that that the PET film contained any material that would cause it to fail the Library specifications.
However, analysis by DART-MS revealed that the PET film was contaminated with erucamide [cis-13-docosenamide], which is a slip agent used in the manufacturing of polyolefin films such as polyethylene and polypropylene. This discovery of erucamide led to a mystery: The manufacturer claimed that neither erucamide nor any other amide slip agent had been used in the manufacture of the PET film. The mystery was solved when the Library staff noted that the PET film had been shipped to the Library enclosed in non-stick, plastic sheet protectors: When the sheet protectors were analyzed by DART-MS, they revealed the presence of erucamide. In contrast, when the Library analyzed new samples of the PET film, sent by the manufacturer enclosed in organic-free aluminum foil, no erucamide was detected.
In summary:
- The Preservation Research and Testing Division has concluded that this PET film meets Library specifications and may be used in archival encapsulations.
- Even though samples of the original PET film were not in direct contact with the non-stick, plastic sheet protectors, the PET samples were nevertheless contaminated with erucamide. This reveals that erucamide migrated from the sheet protectors into the PET film through several layers of PET film.
- PET films that contain amide slip agents would not meet Library of Congress specifications for two reasons. Firstly, there is a high probability that the amide would migrate from the PET film to the object, and due to oxidation, this would likely result in yellowing of the object over time; and secondly, the amide and/or its degradation products might contribute to degradation of the object, with a high probability that the PET itself would yellow over time.
Update and Images: Dr. Jeanette Adams presented this work at the 55th American Society for Mass Spectrometry Conference, 2007
